Wide angle electronic scan luneberg antenna



Dec. 30, 1969 M. w. sHoRl-:s 3,487,413

WIDE ANGLE ELECTRONIC SCAN LUNEBERG ANTENNA Filed DeG. QQ, 1966 2Sheets-Sheet l TMve/Vree Dec. 30, 969 M, w, SHORES 3,487,413

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United States Patent O 3,487,413 WIDE ANGLE ELECTRONIC SCAN LUNEBERGANTENNA Marvin W. Shores, Pomona, Calif., assignor to General DynamicsCorporation, a corporation of Delaware Filed Dec. 30, 1966, Ser. No.606,116

Int. Cl. H01q .Z9/06 U.S. Cl. 343-754 Claims ABSTRACT OF THE DISCLOSUREThis invention is directed to a scanning antenna characterized by a wideangle operational mode and minimum complexity. The illustratedembodiments 4of the `antenna comprise an array of spiral or the likeantennae elements which are grouped in parallel-column fashion andfirmly attached to a Luneberg lens over an arc which is approximatelyequal to one-half of the desired look angle, the individual antennae ofthe array being arranged to face the center of the Luneberg lens andbeing selectively energizable in accordance with a programmed sequenceby way of appropriate pulse controlled gate-switch circuitry. Theinventive antenna may be mechanically rotated by way of an axleextending axially through the Luneberg sphere in order to provide a fullsemi-spherical look angle.

BACKGROUND OF THE INVENTION This invention relates to electromagneticenergy scanning apparatus and more particularly to a wide angle antennawhich utilizes an array of spiral antenna elements operativelypositioned on a Luneberg lens.

A Luneberg lens, as known in the art, is a microwave lens which isspherical in shape and has the property of focusing parallel raysincident upon a side. of the spherical surface, to a point on theopposite surface where a diameter of the sphere, parallel to theincident rays, intersects the opposite surface.

The operation of spiral antennae is known in the art as exemplified byU.S. Patent 3,045,23 7. One explanation of their operation is that eachspiral antenna element behaves as if it were a two wire transmissionline which gradually, by virtue of its spiral geometry, transformsitself into a radiating structure or antenna.

SUMMARY OF THE INVENTION The present invention advances the state of theart relative to the design of search, surveillance and guidancereceivers by providing a wide angle scan antenna which eliminates theintricate mechanism required by the prior art antenna systems to performthe same function.

Therefore, it is an object of this invention to provide a wide anglescan antenna.

A further object of the invention is to provide a wide angle scanantenna which eliminates intricate mechanism required by prior knownantenna systems.

Another object of the invention is to provide a scan antenna whichutilizes a Luneberg lens and a plurality of individually controlledspiral antenna units operatively positioned thereon.

Another object of the invention is to provide a wide angle electronicscan antenna which is capable of providing a full semi-spherical lookangle.

Other objects of the invention will become readily ICC apparent from thefollowing description and accompanying drawings wherein:

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a perspective View of anembodiment of the inventive antenna;

FIG. 2 is an enlarged view illustrating a portion of a three arrayembodiment of the inventive antenna;

FIG. 3 schematically illustrates a portion of the circuitry of theinventive antenna;

FIG. 4 is a view illustrating a full semi-spherical look capability ofthe invention with a narrow beam resolution;

FIG. 5 is a diagrammatc view illustrating the inventive antenna systemfor spherical look operation;

FIG. 6 is a view illustrating the tracking capability of the invention;

FIG. 7 illustrates an embodiment of the invention having multiplefrequency capability; and] FIG. 8 illustrates an embodiment of theinvention for applications requiring a narrow scan angle;

DESCRIPTION OF EMBODIMENTS Referring now to FIGS. 1-3, which broadlyillustrate the inventive antenna, the FIG. 1 antenna consists of aLuneberg lens 10 and a scan array 11 firmly attached t0 the Luneberglens 10 over an arc approximately equal to one half the desired lookangle and over a width determined by the number of parallel arrays. Toprovide a full semispherical look angle the antenna can be mechanicallyrotated about the central axis 12 of the lens 10.

FIG. 2 illustrates a portion of a three array system comprising antennaeelements 13, such as the spiral type, grouped in parallel-column fashionand firmly attached to the Luneberg lens 10 and arranged to face thecenter of the lens. The number of elements 13 depends upon the operatingfrequency, the look angle, and the number of arrays. The elements 13 arepositioned with a cover member indicated at 14 and constructed ofsuitable material such as not to interfere with the operation thereof.

As seen in FIG. 3, the components of antenna elements 13 are shownschematically and each consists of a spiral antenna 15, an electricswitch 16 operatively connected to a control indicated at 17 and tosignal line indicated at 18. The reception angle of the antenna isdetermined by the spiral antenna 15 that is switched on to the signalline 18 by the pulse of the control 17 via switch 16. The pulses fromcontrol 17 may be. programmed as required to scan the look angle of theantenna system.

FIGS. 4 8 and the following description illustrate various applicationsand embodiments of the inventive antenna. In the following descriptionthe term receptor or antenna element designates that the antenna isusable on receivers as well as transmitters.

FIG. 4 illustrates a full semi-spherical look capability with a pencilbeam resolution over the semi-spherical lield of view. A Luneberg lens20 is provided with a single row of receptors or antenna elements 21-30arranged on the circumference of the lens 20 over a 90 quadrant. Withthe receptor 21 on and the receptors 22-30 oli the receive or radiatepencil beam would appear as indicated at 21'. Next receptor 22 isswitched on and 21 and 23 through 30 are olf producing a beam 22. Thereceptor or antenna elements 21-30 may be spaced such as to overlapbeams 21'-30 at some arbritrary point, in the case illustrated at theone-half power points. The receptors 21-30 are switched on and off insequence until a complete look through receptor 30 via beam 30 iscompleted, and the sequence is then repeated.

With the lens/receptor arrangement as illustrated in FIG. 4, theassembly is rotated about its axis 31 by suitable means, such as shownin FIG. 5 at 32, such that receptor 30 shifts an angle less than thebeam width between the one-half power points in this case. The receptors21 through 30 are again sequentially switched on and the rotationcontinued until the total area of the 180 semi-sphere has been sampledor radiated. In actual practice the assembly rotation would necessarily-he limited to some practical rate, for example, 60 or 120 revolutionsper minute or one or two revolutions per second. The receptor or antennaelement sample or radiate rate, being electronic, may, for example, bein the order of one megacycle per second. Thus, for one-r.p.s. rotationrate and receptor scan rate of one mc./s., each one of the elements21-30 would be sampled 100,000 times per revolution of the antennaassembly.

It should be noted that the antenna field of View is not limited to a180 semi-sphere. Beyond 180 some shadowing of the lens 20 aperture wouldoccur because of further wrap around of the receptor or antenna assembly13 as shown in FIG. 5. In certain applications this degradation may benegligible and a full hemispherical field of View is possible.

The invention antenna also -has the capability of beaming at any pointin a hemispherical field of view. To point the antenna at apredetermined area in space, the FIG. 4 assembly, for example, isrotated to designated position and the appropriate receptor or antennaelement 21-30 is enabled or turned on while all other of the receptorsare offf This feature simulates a parabolic antenna, being pointed bymechanical linkage or gear drive systems.

FIG. 6 illustrates how radar target or object tracking capability can beperformed by an embodiment of the inventive concept. This technique isreferred to as lobing and consists of a Luneberg lens 40 with a doublereceptor array of elements 41-50 and 51-60 operably mounted thereon,lens 40 being rotatable about an axis or axle 52. If, for example, atagret was located in the field of view relative to the convergent pointx at the left, the antenna would Ibe switched as shown in FIG. 6 aboutthis point.

If the convergent remains dead center of receptor elements 44, 54, 45and l55, as shown, the signal power return from each element wouldappear relatively equal. When the target moves in the field of view theconvergent point x would also move and the double array 41-50 and 51-60would thereby cause an unbalance 50 in the signal power received in eachof these four elements (44, 54, 45 and '55). The unbalance would beprocessed and corrective action generated to rotate the antenna tomaintain proper tracking.

The inventive antenna concept is capable of multiple frequency bandoperation at a maximum eliiciency for a given diameter lens. For eachfrequency -band a separate array is provided as illustrated in FIG. 7wherein the elements or spiral antenna for each of the frequency bandsdiffer in dimension. For example, a Luneberg lens is provided with a Cband 61-68, an X band 71-80, and a P band 6172', each of the frequencybands extending outwardly from an axis 81 over an arc approximatelyequal to one-half the look angle.

The inventive concept can also be readily utilized in applications wherea narrow scan angle is accetpable and antenna gain degradation atextreme angles off the bore sight is acceptable, a half lens design maybe used as shown in FIG. 8. As shown in FIG. 8, an antenna array 4 onthe virtual image principle which is known in the art and, for example,is described in U.S. Patent 2,835,891. As illustrated in FIG. 8, withelement 99 on an amount of aperture area is lost as indicated at 104,while with element 91 on maximum gain would be provided.

A spiral scan of the field of view is another capability of theinventive concept. For example, with the FIG. 4 embodiment, receptor orantenna element 21 would 4be left on for a full rotation of the lens 20,then element 22 is switched on during the second revolution and soforth, until the entire field has been examined by each of the receptors21-30. The sequence would then be repeated.

While the receptors or antenna elements have been described as being ofthe spiral type, different types 0f antenna elements, both polarized andnon-polarized, may be utilized depending on the application. Forexample, a radar-receiver application could utilize polarized slots ordipoles, while a surveillance receiver or a semi-active guidance systemmay have to be non-polarized.

It has thus been shown thatrthis invention provides an antenna systemwhich substantially advances the state of the art and eliminates theintricate mechanism that is required by the prior known antenna systemsto perform the same function. In addition, the scan rate of thls antennacan exceed the rate attainable by the known systems by severalmagnitudes.

Although particular embodiments of the invention have been illustratedand described, modifications and changes will become apparent to thoseskilled in the art, and it is intended to cover in the appended claimsall such modifications and changes as come within the true spirit andscope of the invention.

What is claimed is:

1. An antenna system including a microwave spherical Luneberg lens forfocusing electromagnetic energy, an array of spiral antenna elementspositioned on the spherical surface of the lens over an arc at leastapproximately equal to one-half of the desired look angle, means forselectively energizing said antenna elements, and means for moving saidlens about an axis through the sphere which lies in the plane of thespiral antenna arc.

2. The antenna system defined in claim 1, wherein said microwave lens isa Luneberg spherical type, and wherein said antenna elements are 0f thespiral type.

3. The antenna system defined in claim 1, wherein said array of antennaelements is grouped in a three columnparallel arrangement.

4. The antenna system defined in claim 1, wherein said array of antennaelements is grouped in a two column-parallel arrangement.

5. The antenna system defined in claim 1, wherein said means forselectively energizing said antenna eleme'nts includes electronic switchmeans for each of said antenna elements, and control means for directingcontrol pulses to said switch means for operating sarne.

6. The antenna system defined in claim 1, wherein said microwave lens isof a Luneberg spherical type, and wherein said array of antenna elementscomprises a single column of elements extending across about of saidLuneberg lens.

7. The antenna system defined in claim 1, wherein said array of antennaelements is composed of a plurality of columns of antenna elementsextending outwardly from said axis, at least certain of said columnsbeing operable in different frequency bands.

8. The antenna system defined in claim 1, wherein said microwave lens isof the Luneberg type and is of a semi-spherical configuration, said lensbeing provided with a reflector means across the fiat surface thereof,the axis of movement of said lens extending in a direction substantiallyperpendicular to the flat surface of said lens, and wherein said arrayof antenna elements is a column on one side of said axis of movement.

9. The antenna system defined in claim 1, wherein said microwave lens isof a -Luneberg spherical type, wherein said antenna elements are of thespiral type, and wherein said means for selectively energizing saidantenna elements includes electronic switch means lfor each of saidantenna elements and control means for activating and deactivating saidswitch means, whereby said antenna elements may be programmed tosequentially scan the desired look angle of the antenna during movementof saidlens` References Cited UNITED STATES PATENTS 7/1962 Marston343-895 12/1963 Johnson et al. 343-911 1/ 1966 `Cheston 343-754 11/1966Atlas 343-911 5/1968 List et al. 343-911 11/1968 Young 343-754 10. Theantenna system defined in claim 9, wherein 10 ELI LIEBERMAN PrimaryExaminer said array of antenna elements is congured in a single columnand positioned so as to overlap adjacent beams at the one-half powerpoints.

U.S. C1. X.R.

